Combining multiple-subaperture and two-wavelength techniques to extend the measurement limits of an optical surface...

A method has been developed for extending the measurement range of an optical surface profiler using the techniques for combining multiple subapertures and two-wavelength phase-shifting interferometry. The effective trace length of the optical profiler is augmented by making a series of partially overlapping collinear measurements and then piecing the subapertures into a composite profile, thus extending the field of view of the instrument. The vertical dynamic range of the optical profiler is extended by taking phase measurements at two wavelengths and then subtracting these measurements to obtain the same result as if the object had been tested at a longer equivalent wavelength. This allows the resolution of phase ambiguities that may exist when using single-wavelength phase-shifting interferometry. Combining these techniques offers numerous possible applications for testing deep wave fronts and surfaces, such as aspheric optical components, with variable sensitivity.